When to Avoid the text-decoration Shorthand Property | CSS-Tricks

In my recent article about CSS underline bugs in Chrome, I discussed text-decoration-thickness and text-underline-offsettwo relatively new and widely-supported CSS properties that give us more control over the styling of underlines.

Let me demonstrate the usefulness of text-decoration-thickness on a simple example. The Ubuntu web font has a fairly thick default underline. We can make this underline thinner like so:

:any-link {
  text-decoration-thickness: 0.08em;
}
Showing two links, a default and one that decreases the text-decoration-thickness.

/explanation throughout this article, I will use the :any-link selector instead of the a element to match hyperlinks. The problem with the a tag as a selector is that it matches all <a> elements, even the ones that don’t have a href attribute and thus aren’t hyperlinks. The :any-link selector only matches <a> elements that are hyperlinks. Web browsers also use :any-link instead of a in their user agent stylesheets.

Hover underlines

Many websites, including Google Search and Wikipedia, remove underlines from links and only show them when the user hovers a link. Removing underlines from links in body text is not a good idea, but it can make sense in places where links are more spaced apart (navigation, footer, etc.). With that being said, here’s a simple implementation of hover underlines for links in the website’s header:

header :any-link {
  text-decoration: none;
}

header :any-link:hover {
  text-decoration: underline;
}

But there’s a problem. If we tested this code in a browser, we’d notice that the underlines in the header have the default thickness, not the thinner style that we declared earlier. Why did text-decoration-thickness stop working after we added hover underlines?

Let’s look at the full CSS code again. Can you think of a reason why the custom thickness doesn’t apply to the hover underline?

:any-link {
  text-decoration-thickness: 0.08em;
}

header :any-link {
  text-decoration: none;
}

header :any-link:hover {
  text-decoration: underline;
}

The reason for this behavior is that text-decoration is a shorthand property and text-decoration-thickness its associated longhand property. Setting text-decoration to none or underline has the side effect of re-initializing the other three text decoration components (thickness, styleand color). This is defined in the CSS Text Decoration module:

The text-decoration property is a shorthand for setting text-decoration-line, text-decoration-thickness, text-decoration-styleand text-decoration-color in one declaration. Omitted values ​​are set to their initial values.

You can confirm this in the browser’s DevTools by selecting one of the hyperlinks in the DOM inspector and then expanding the text-decoration property in the CSS pane.

DevTools screenshot showing text-decoration styles on the :any-link pseudo-selector.

In order to get text-decoration-thickness To work on hover underlines, we’ll have to make a small change to the above CSS code. There are actually multiple ways to achieve this. We could:

  • set text-decoration-thickness after text-decoration,
  • declare the thickness in the text-decoration shorthand, or
  • use text-decoration-line instead of text-decoration.

Choosing the best text-decoration option

Our first thought might be to simply repeat the text-decoration-thickness declaration in the :hover state. It’s a quick and simple fix that indeed works.

/* OPTION A */

header :any-link {
  text-decoration: none;
}

header :any-link:hover {
  text-decoration: underline;
  text-decoration-thickness: 0.08em; /* set thickness again */
}

However, since text-decoration is a shorthand and text-decoration-thickness is its associated longhand, there really should be no need to use both at the same time. As a shorthand, text-decoration allows setting both the underline itself and the underline’s thickness, all in one declaration.

/* OPTION B */

header :any-link {
  text-decoration: none;
}

header :any-link:hover {
  text-decoration: underline 0.08em; /* set both line and thickness */
}

If this code looks unfamiliar to you, that could be because the idea of ​​using text-decoration as a shorthand is relatively new. This property was only turned into a shorthand in CSS Text Decoration module. In the days of CSS 2, text-decoration was a simple property.

Unfortunately, Safari still hasn’t fully caught up with these changes. In the WebKit browser engine, the shorthand variant of text-decoration remains prefixed (-webkit-text-decoration), and it doesn’t support thickness values ​​yet. See WebKit bug 230083 for more information.

This rules out the text-decoration shorthand syntax. The above code won’t work in Safari, even if we added the -webkit- prefix. Luckily, there’s another way to avoid repeating the text-decoration-thickness declaration.

When text-decoration was turned into a shorthand, a new text-decoration-line longhand was introduced to take over its old job. We can use this property to hide and show the underline without affecting the other three text decoration components.

/* OPTION C */

header :any-link {
  text-decoration-line: none;
}

header :any-link:hover {
  text-decoration-line: underline;
}

Since we’re only updating the line component of the text-decoration value, the previously declared thickness remains intact. I think that this is the best way to implement hover underlines.

Be aware of shorthands

Keep in mind that when you set a shorthand property, eg, text-decoration: underline, any missing parts in the value are re-initialized. This is also why styles such as background-repeat: no-repeat are undone if you set background: url(flower.jpg) afterwards. See the article “Accidental CSS Resets” for more examples of this behavior.

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